This application is based on Japanese Patent Application No. 2004-345149 filed on Nov. 30, 2004.
1. Field of the Invention
The present invention relates to a sheet post-processing apparatus which performs a sheet sorting process, a sheet stapling process, or the like after image forming.
2. Description of the Prior Art
For example, there may be a case where a binding process (hereinafter referred to as a stapling process) and a holing process (hereinafter referred to as a punching process) are desired to be performed on a relatively large volume of sheets of paper bearing an image transferred thereon by an image forming apparatus such as a copying machine or a printer. In such a case, it is convenient to use a sheet post-processing apparatus or a so-called finisher that automatically performs a predetermined post-processing, such as a stapling process and a punching process.
FIG. 7 is a side sectional view showing an example of configuration of a known sheet post-processing apparatus. In FIG. 7, a sheet post-processing apparatus 1 includes a processing tray 2 capable of accommodating a plurality of sheets P and detachably connected, for example, on a sheet discharging side of an image forming apparatus (not shown in the drawing) such as a copying machine. In the case where a stapling process or the like is performed on sheets sequentially discharged from the image forming apparatus, each of the sheets P is once accommodated in the processing tray 2. A pair of introducing rollers 3 is provided on the upper right portion of the processing tray 2, and the sheets P discharged from the image forming apparatus are fed inside the sheet post-processing apparatus 1 via the pair of introducing rollers 3 and introduced on the processing tray 2 through the introducing port 4.
Further, the processing tray 2 is provided with a bundle edge aligning hook 9 movable along the processing tray 2. The bundle edge aligning hook 9 waits at the lower end of the processing tray 2 when the sheets are introduced, and one end of the sheets P, in a feeding direction, that are sequentially introduced onto the processing tray 2 from the pair of introducing rollers 3 is supported by the bundle edge aligning hook 9. In the vicinity of a waiting position of the bundle edge aligning hook 9, an end binding stapler 5 is provided. The end binding stapler 5 performs a stapling process on one set of the sheets P whose end portions in the feeding direction are aligned by the bundle edge aligning hook 9. The sheets P in which the stapling process is completed are fed to the upside of the sheet post-processing apparatus 1 along the processing tray 2 by the bundle edge aligning hook 9 to be discharged to a discharging tray 7 via the bundle discharging rollers 6.
In such a sheet post-processing apparatus, in the case where post-processing such as a stapling process or the like is sequentially performed, processing waiting time occurs because new sheets cannot be introduced to the processing tray 2 during a post-processing operation. Particularly, in the case of sheets of general-purpose A4 size, time intervals between the sheets are minimized so as to be capable of high-speed image forming process. However, post-processing operation has been inefficient due to the processing waiting time in the sheet post-processing apparatus.
Furthermore, in the case where a relationship between the position of the introducing port 4 and the waiting position of the bundle edge aligning hook 9 is not suitable to a feeding direction length of the sheets P, a subsequent sheet could slip in the rear side (on the left side in the drawing) of the sheet previously introduced in the processing tray 2, thereby changing the order of the sheets. Therefore, the introducing port 4 needs to be moved depending on the sheet size; however, this separately requires a driving system for moving the introducing port 4, thereby making the configuration of the device complicated, as well as resulting in increased size and cost of the device.
Consequently, various methods have been proposed to solve the aforementioned problems. Japanese Examined Patent Application No. H06-99070 discloses a sheet processing apparatus in which arrival of a first preceding sheet to sheet processing means is delayed, thereby making the first sheet arrive the processing means in an overlapped state with the subsequent sheet, whereby waiting time can be eliminated as being acceptable for new sheets even when the processing means is during processing operation. Further, Japanese Patent No. 2783326 discloses a post-processing apparatus in which sheets are discharged to a discharging tray on the upper side when a stapling process is not performed; and when a stapling process is performed, a reference side fence of the stapler is moved depending on the sheet size to discharge to a second discharging tray on the lower side by performing the stapling process without moving sheets.
Moreover, Japanese Unexamined Patent Application No. 11-263502 discloses a sheet post-processing apparatus that is provided with different introducing ports for sheets of different sizes to be fed and branching claws corresponding to different lengths of the sheets in the feeding direction, and that prevents the sheets from slipping-in by changing feeding paths by swaying the branching claws so as to feed the sheets to the processing tray from a position corresponding to the size of the sheet.
In the case of so-called middle-binding which performs a stapling process on the middle portion of a bundle of the sheets, it is required to use a separated type stapler in which an ejecting portion of a stapling needle and a receiving portion are separated; and, in the case of a known sheet post-processing apparatus capable of performing end-binding and middle-binding, a separated type stapler for both end-binding and middle-binding is disposed in the central vicinity of the processing tray 2. However, in the case where both the end-binding process and middle-binding process are performed on the processing tray 2, introducing paths for sheets are complicated and easy to generate a jam on the processing tray 2.
Still, generally, the bundle of the sheets performed by middle-binding is simultaneously performed by middle-folding process to be in a brochure form and therefore a middle-folding device is required to be provided adjacent to the processing tray 2; however, it is difficult to secure a sufficient arrangement space. Further, the number of capable of binding of a separated type stapler is less compared to that of an integrated stapler and therefore, in the case where an exclusive color printing paper whose paper surface is hard due to especially surface finishing is used, a stapling process cannot be performed by the number of capable of processing guaranteed in the case of a plain paper and it is difficult to perform both middle-binding and end-binding by the separated type stapler.
According to Japanese Examined Patent Application No. H06-99070 and Japanese Patent No. 2783326, waiting time for accepting sheets and loss of moving time of sheets and a stapler are resolved to accelerate processing, but the aforementioned problems have not been solved. Furthermore, it may be taken into account that the number of capable of processing is increased using a large separated type stapler and an integrated stapler for end-binding is separately provided in addition to a separated type stapler; however, since arrangement space is limited in the vicinity of the processing tray 2, it is difficult to increase the stapler in size and to arrange two staplers. Further, according to Japanese Unexamined Patent Application No. 11-263502, since a plurality of branching claws need to be provided for different sheet sizes and to be switched, there is a problem in that a structure of the feeding paths is complicated.